1. Field of the Invention
The present invention related generally to a light source structure and a scanning window structure of a scanner, and more particularly to a structure of a uniform light source for a book scanner. The scanning window has an angled structure so that two adjacent pages of a book may be placed closely onto the scanning window when the book is open. The light source is strip-shaped light source that moves along the crest line of the scanning window to provide uniform light required to scan the book.
2. Description of the Prior Art
Conventional scanners comprise a housing, a scanning window, a carriage module, and a light source. The scanning window is disposed on the top of the housing, the carriage module is disposed moveably in the housing, and the light source is disposed on the carriage module and opposite to the scanning window. The light from the light source penetrates the scanning window and illuminates the sheet to be scanned on the scanning window.
The light source is a strip-shaped tubular light source. Theoretically illumination on each scan line at each position of the surface of a sheet is same when a light source is disposed in parallel to a flat scanning window. However, practically, the luminous intensity at both ends of a tubular light source is less than the luminous intensity in the middle thereof, and the luminous intensity is more uniform in the area approaching the middle part of the light tube.
As FIG. 6 shows, one end of the light tube is defined section A and the other end of the light tube is defined section C, and the middle portion of the light tube is defined section B. The luminous intensity variation of Section A and Section C are much greater than the Section B. It means that the luminous intensity of the two ends of the light tube is uneven. For a scanner with an uneven light source, compensation will be provided for a carriage module to calibrate the image sensing signal. (Refer to FIG. 6 for ideal intensity calibration curve.) However, the difference between the actual luminous intensity and desired calibrated intensity of the light source becomes greater when the entire light tube is used as the light source, even greater than the effective compensation of the light source in the scanner. In FIG. 6, L stands for the actual maximum intensity of the light source, while L1 is the difference between the ideal calibrated intensity and the actual maximum intensity of the light source. When L1/L/⅓, or even L1/L/½, the calibration result of the carriage module is not to meet the requirement with the current light source compensation of the scanner. In the circumstances, the scan image corresponding to both ends of the light source is vague or incorrect and, thus, does not meet the requirements for high image quality.
Images of poor scan quality brought by low and unstable luminous intensity at the two ends of the light source occurs especially for book scanners. In FIG. 1, the book scanner 10 includes a housing 12 and a scanning window 14. The scanning window 14 with an angular structure is disposed on the housing 12. A carriage 15 with two sets of scanning modules 16 moving reciprocatingly is disposed in the housing 12. The scanning window 14 has two light transmission parts 142 and 144 so that two adjacent pages of a book 18 may be placed closely onto the surface of the light transmission parts 142 and 144 when the book is open. Each scanning module 16 is disposed under the light transmission part 142 or 144, and the scanning module 16 is parallel to the light transmission part 142 or 144. The scanning module 16 includes two reflective mirrors 162 and 163, a lens 164, a image sensor 166, and a light source 168.
As shown in FIG. 1, the light from each light source 168 illuminates the binding section 182 of the book 18. Since the luminance of both ends of the light source 168 is low and unstable, the scan images produced at the binding section 182 of the book 18 and at the edge thereof are blurred or incorrect.